This invention relates to wire dot printers and, more particularly, to an ink composition and a wire dot printer including the composition.
Conventional wire dot printers utilize an ink ribbon for transferring ink onto recording paper. There are, however, drawbacks to using such conventional wire dot printers. The useful life of an ink ribbon is short and consequently the ribbon must be changed frequently. Additionally, it is necessary to provide a feeding mechanism for feeding or advancing the ink ribbon in order for the printer to function properly, and therefore, the structure of the printer is more complex. Furthermore, print density of the ink ribbon at the beginning is different compared to the end of the ink ribbon.
In order to avoid such shortcomings in the art, an ink wire dot printer can transfer ink onto a recording paper by placing the ink directly on a wire tip without using an ink ribbon. Such ink wire dot printers transfer ink from an ink tank to the wire tip by an impregnation member, a capillary tube or pump mechanism. Various methods, for example, are disclosed in applicant's Japanese laid-open Application No. 164,173/1980, Japanese laid-open Application No. 6783/1982, U.S. Application No. 502,857, Japanese Utility Model Publication No. 2652/1978 and U.S. Pat. No. 4,194,846. The ink compositions disclosed include principally a polyhydric alcohol wetting agent and water.
The use of water as the solvent of an ink composition in an ink wire dot printer has many disadvantages. The head of an ink wire dot printer is an open type of structure. It is difficult to provide a closed structure for such a device to avoid ink drying as in the case of an ink jet head. Thus, when the head is left unused for a period of time, the water in the ink will evaporate. Additionally, the ink solvent which is at the periphery of the distal end of the wire will become highly viscous, reducing the ink's fluidity. Furthermore, as water continues to evaporate, sufficient ink cannot be transferred onto a recording paper by the wire so that the dots are lightly printed and finally, the shape of the ink dot formed is improper. In this case the ink will not permeate the paper surface and remains thereon after printing as the surface tension is too high. In extreme cases, when the ink is allowed to dry for a long period of time, the wire of the ink printer becomes clogged and the printing device cannot be used at all.
Japanese laid-open Application No. 75874/1981 discloses a method for preventing ink from drying by covering the wire portion of the printer head when not in service. However, this method requires removal of the cover when operation begins and reattachment of the cover when operation concludes. The user of such a device is substantially inconvenienced each time the printer is used. Accordingly, it is desirable to provide an ink wire dot printer and an ink composition used in the printer which will not dry out when exposed to the air. This type of ink is desirable because no special structure is necessary to maintain workability of the printing machine.